As a method replacing a conventional radiography, a radiation image recording and reproducing method utilizing a stimulable phosphor as described, for instance, in U.S. Pat. No. 4,239,968, was proposed and has been practically employed. In the method, a radiation image storage panel comprising a stimulable phosphor (i.e., stimulable phosphor sheet) is employed, and the method involves the steps of causing the stimulable phosphor of the storage panel to absorb radiation energy having passed through an object or having radiated from an object; sequentially exciting the stimulable phosphor with an electromagnetic wave such as visible light or infrared rays (hereinafter referred to as"estimulating rays") to release the radiation energy stored in the phosphor as light emission (i.e., stimulated emission); photoelectrically detecting the emitted light to obtain electric signals; and reproducing the radiation image of the object as a visible image from the electric signals. The radiation image storage panel thus treated is subjected to a step for erasing a radiation image remaining therein, and then is stored for the next radiation image recording and reproducing procedure. Thus, the radiation image storage panel is repeatedly employed.
In the radiation image recording and reproducing method, a radiation image is obtainable with a sufficient amount of information by applying a radiation to an object at a considerably smaller dose, as compared with the conventional radiography using a combination of a radiographic film and radiographic intensifying screen. Further, the radiation image recording and reproducing method using a stimulable phosphor is of great value especially when the method is employed for medical diagnosis. Furthermore, the radiation image recording and reproducing method is advantageous in saving resources and economical efficiency, as compared with the conventional radiography, because the radiation image storage panel is repeatedly employed, while a radiographic film is employed only for one shot.
The radiation image storage panel employed in the above-described method has a basic structure comprising a support and a stimulable phosphor layer provided on one surface of the support. If the phosphor layer is selfsupporting, however, the support may be omitted.
The stimulable phosphor layer generally comprises stimulable phosphor particles and a binder. Stimulable phosphor layers of other types are also known. For instance, a stimulable phosphor layer comprising agglomerated stimulable phosphor particles and no binder can be prepared by a sintering method or a vacuum deposition method. The agglomerated stimulable phosphor layer can contain a polymer, if desired. Any of radiation image storage panels having these stimulable phosphor layers can be employed in the above-described radiation image recording and reproducing method.
Further, a transparent film of polymer material is generally provided on the free surface (surface not facing the support) of the phosphor layer to keep the phosphor layer from chemical deterioration or physical shock. The protective film can be provided, for instance, by coating a solution of a transparent organic polymer such as a cellulose derivative or polymethyl methacrylate on the phosphor layer, by fixing a beforehand prepared polymer film such as a polyethylene terephthalate film on the phosphor layer with an adhesive, or by vacuum depositing inorganic material on the phosphor layer.
The coated protective layer can be readily prepared by coating a solution of polymer material on the phosphor layer, and the coated protective layer is firmly fixed on the phosphor layer.
In the radiation image recording and reproducing method, the radiation image storage panel is repeatedly employed in the steps of radiation of X-rays (recording of radiation image), irradiation of stimulating rays (reading out of the recorded radiation image), and exposure to erasing light (erasure of residual radiation image). Between these steps, the storage panel is transferred by conveyors such as belts and/or rollers within the apparatus for performing the radiation image recording and reproducing method. When these steps are repeated, the coated protective layer of the storage panel is apt to be stained or to receive abrasions or scratches on its surface. The stains, abrasions, and/or scratches produced on the surface of the protective layer causes deterioration of image quality of a reproduced radiation image. The radiation image storage panel naturally is desired to give a reproduced radiation image of high quality (such as high sharpness and improved graininess). Therefore, the production of stains, abrasions and scratches on the surface of the protective layer should be avoided.
Japanese Patent Provisional Publication No. 2(1990)-193100 (corresponding to U.S. patent application Ser. No. 07/704,738) describes a protective film of a fluororesin which is soluble in an organic solvent and is coated on a stimulable phosphor layer of a radiation image storage panel. The protective film of a fluororesin can effectively reduce the production of stains, abrasions and scratches.
U. S. Pat. No. 5,227,253 discloses a radiation image storage panel having a protective film which is produced from a mixture of a film-forming resin (such as a fluororesin) and an oligomer having a polysiloxane skeleton or a perfluoroalkyl group. The protective film of a mixture of the fluororesin and others can more effectively reduce the production of stain, abrasions and scratches.